Injectors are a commonly used device for injecting fuel into the cylinders of an internal combustion engine. One of the ways to improve the efficiency of an engine is to inject the fuel in an “atomized” form. Fuel that is atomized burns much more efficiently, allowing as much of the fuel to be used as possible.
Different fuel injectors are often used with different types of fuel, which have different material properties, and react differently to various temperature changes. One such type of fuel is ethanol, which freezes or solidifies during cold weather conditions. Many attempts have been made to improve the operation of a fuel injector used with ethanol to eliminate freezing of the ethanol.
Spray generation, or atomization, is created by the fluid stream breaking into droplets, while being directed in a specific direction. Breakup of the fluid stream is further enhanced by keeping the fluid turbulent as it exits the orifice hole. One of the factors that influence the atomization of the fluid is the shape of the exit orifice or exit aperture through which the fluid passes as the fluid exits the injector. Some injectors include a plate which may have several exit apertures through which the fluid passes. If the fluid flow becomes laminar, or streamlined, to the wall of the exit aperture, the fluid droplets become elongated and create large droplets, or “ligaments.” The definition of the size of a ligament is quantified by the particle size measurement of Sauter Mean Diameter (SMD).
One of the contributing factors to this particle size is the ratio of the material thickness or depth of the wall of the exit aperture to the diameter of the wall of the exit aperture, referred to as the L/D ratio. As the depth or thickness of the exit aperture is minimized, atomization is improved. However, using a plate which is of a single thickness and minimizing the thickness of the exit aperture to improve atomization also requires that the material used to create the plate be minimized in thickness as well, which then reduces the weld properties of the plate, increasing the difficulty in welding the plate to the injector during assembly.
When the thickness of the exit aperture is above a certain value, such as 0.006 inches, and the L/D ratio approaches 1.0, the fluid, or fuel in liquid form, reattaches to the wall of the aperture, causing ligaments and larger droplets. The ligaments often build up in the injector, which causes problems during cold starts.
Accordingly, there is a need for a plate having an exit aperture or orifice used in a fuel injector which reduces droplet size, and therefore reduces or eliminates the formation of ligaments and large droplets, where the plate still maintains desirable weld properties.